1. Field of the Invention
This invention pertains to connectors for tubular goods and more particularly to such connectors employing a coupling for making the connection between two joints or lengths or pipe which are aligned for coupling pin end to pin end.
2. Description of the Prior Art
Tubular goods used in oil and gas production generally comprise production tubing and casing. The tubular goods discussed herein are particularly well suited for such an environment and conditions of such an environment will be referred. However, the inventive coupling described and claimed herein has general application to tubular goods and therefore is not limited to such a use application.
It is quite normal for joints or lengths of tubular goods to include a pin end and a box end and to be joined to adjacent joints so that a pin end of one joint fits into the box end of the adjacent joint. In such an arrangement, the connection is referred to as an "integral" connection and no auxiliary coupling member is required.
There are two ordinary ways of constructing or manufacturing the box end, both ways entailing a change in the metallurgy of the material. A first way is by an "upsetting" technique, which is achieved at high temperature and stressing above the heated yield point of the metal. A second technique is referred to as "cold forming" or "swaging" and is not performed at elevated temperature, but does involve taking the metal beyond its yield point and introducing stresses in the metal. Some of these stresses can be relieved in a subsequent heat treatment step. However, it is well-known that even after such a step there are still permanent changes in the physical properties of the metal compared to its condition before being so worked. Various terms have been given to the resultant metal condition such as being "work-hardened", being susceptible to "hydrogen embrittlement" or being subject to "sulfide stress cracking".
Further, threads can take on numerous forms. One of the more popular forms in recent years has been the so-called "dove-tail thread", as described in U.S. Pat. No. Re. 30,647, reissued June 16, 1981, and entitled "Tubular Connection", in the name of Thomas L. Blose, which is incorporated herein by reference for all purposes. Such a thread construction causes the box connecting end to be radially pulled in and the pin connecting end to be radially pulled outwardly during makeup as the gradually width increasing helical threads are made up and the flank portions of the threads come into wedge-type contact.
It should be noted that in the threads described in U.S. Pat. No. Re. 30,647 there is appreciable space between the root and crest portions of the threads when the connection is made up. This is an acceptable condition since metal-to-metal pressure seals in most connections employed in "premium" applications are not made within the threads themselves, but at conical sealing surfaces adjacent the threads or thread sets in the case of staggered thread configurations. "Premium" situations are those situations which are at the large pressure conditions that are ordinarily encountered at greater well depths.
Heretofore, there has not been a suitable connection for "non-premium" and "semi-premium" applications that have the advantages of wedge threads and which also avoid the use of a work-hardened component. A "non-premium" application may conveniently be defined for a well depth up to about 7500 feet where the pressure encountered is relatively low, i.e., less than about 5000 psi. "Semi-premium" applications are encountered for well depths between about 7500-15,000 feet for pressure less than about 10,000 psi.
Therefore, it is a feature of the present invention to provide in one preferred embodiment an improved tubular connection using wedge threads that provide a metal-to-metal seal and an auxiliary coupling with a machined bore structure that allows a pin-end-to-pin-end connection without employing a work hardened component.
It is another feature of the present invention to provide such a coupling connection where a conical metal-to-metal sealing surface is achieved in addition to the thread seal.
It is still another feature of the present invention to provide such a coupling connection where the conical sealing surface if provided with a groove and elastomeric sealing ring which achieves a compound wedge seal with the conical sealing surface.
It is yet another feature of the present invention to provide such a coupling connection including a corrosion barrier ring between the tips of the pin ends within the bore of the coupling.